PET/CT中CT仿真人体模型的图像质量与辐射剂量关系的研究

目的 以仿真人体模型为实验对象，研究PET/CT中CT图像质量与辐射剂量的关系，为保证图像质量同时降低受检者的辐射剂量提供数据依据。方法 用美国GE Discovery ST型 PET/CT，对仿真人体模型（Model RS-550）进行扫描。CT采集条件：管电压120 kV，管电流30~250 mA范围内11种固定值及自动管电流，螺距（pitch）分别为0.938、1.375、1.75，模拟临床PET/CT的全身扫描方式对仿真人体模型进行扫描。对图像进行分析，计算腹部主要器官的噪声、信噪比及质量因数。结果 噪声随有效剂量的增加而降低，有效剂量<15 mSv时，噪声变化幅度较大；>15 mSv时，噪声变化缓慢。信噪比、对比信噪比随有效剂量增加而增加。相同的有效剂量时，质量因数与扫描方案相关。自动管电流模式下的所有指标，均优于固定管电流采集模式。结论在CT图像质量达到一定程度后，进一步增加有效剂量，图像质量提高有限。根据不同的临床需求在保证一定图像质量的前提下，选择适当的CT扫描方案，降低受检者的有效剂量。

Effect on image quality and radiation dose in a phantom study for PET/CT

Objective To investigate the effect on image quality and radiation dose of PET/CT with Anthropomorphic phantom to provide data basis for decreasing the radiation dose. Methods PET/CT system of GE Discovery ST-16 was used to scan the anthropomorphic phantom (Model RS-550). CT acquisition conditions were as follows: tube voltage 120 kV, tube current 30-250 mA, pitch 0.938, 1.375 and 1.75. Scan range was divided into body scan and head-neck scan to simulate clinical PET/CT. The noise (SD) was recorded and the signal-to-noise ratio and the figure of merit were calculated. Results The noise decreased with increasing effective dose. The noise decreased rapidly with the effective dose less than 15 mSv, while the decrease of noise was not significant with the effective dose more than 15 mSv. The signal-to noise ratio increased with increasing effective dose. However, the figure of merit was fixed, when the radiation dose increased under the different acquisition condition. All indicators of ATCM were superior to the fixed tube current mode. Conclusions The image quality of CT in PET/CT could not significantly improve by increasing effective dose when it reaches to certain level. It shows that the radiation dose of PET/CT could be effectively reduced by appropriate acquisition conditions according to different clinical requirements.